The present invention relates to an apparatus for and a method of controlling an automatic transmission, particularly to the technology of restraining a racing during a speed change.
There has been known a conventional automatic transmission constructed to perform a speed change by a friction engagement element replacement for carrying out simultaneously an engagement control and a release control of two friction engagement elements.
As an apparatus for controlling a speed change of the above construction, as disclosed in Japanese Unexamined Patent Publication No. 11-030324, there is known a construction where an accumulator is disposed in piping for supplying oil pressure to each friction engagement element, and a back pressure of the accumulator is controlled, thereby restraining a change speed of the oil pressure.
Technologies to restrain an occurrence of a racing during speed change are disclosed in Japanese Unexamined Patent Publication Nos. 7-012210, 5-039843, and 2000-055180.
In the technology disclosed in Japanese Unexamined Patent Publication No. 7-012210, a rise in oil pressure in an engagement side friction engagement element is detected by a pressure switch and drain timing of oil pressure in a release side friction engagement element is determined based on the detection result.
In the technology disclosed in Japanese Unexamined Patent Publication No. 5-039843, an oil pressure of a release side friction engagement element is increased when a slip amount of the release side friction engagement element is a threshold value or above, while the oil pressure is decreased when a variation ratio of the slip amount is 0 or less.
Further, in the technology disclosed in Japanese Unexamined Patent Publication No. 2000-055180, a stroke completion in the engagement side friction engagement element is estimated and a decrease in line pressure is started in accordance with the stroke completion.
However, in the construction where the pressure switch is used, there is caused a problem in that a system cost of the automatic transmission has risen since the pressure switch is expensive in general.
Further, in the construction where the oil pressure is controlled corresponding to the slip amount of the release side friction engagement element, the speed change performance is likely to deteriorate due to prolongation of speed change period since the racing is conversed by controlling the oil pressure so as to maintain an extremely small slip amount.
Moreover, in the construction where the decrease in line pressure is started in accordance with the stroke completion of the engagement side friction engagement element, there is caused a problem in that an occurrence of racing cannot be stably restrained due to an estimation error at a stroke completion period, and also there is a possibility that the decrease in line pressure in a torque phase lowers the response performance of a clutch oil pressure, thereby promoting the further racing.
As disclosed in Japanese Unexamined Patent Publication No. 11-030324, in the construction where the drain timing of the accumulator back pressure in the release side friction engagement element is controlled with the accumulator back pressure in the engagement side as a reference, since oil in the friction engagement element and in an oil passage drains during a vehicle is left without a driver, when the speed change is conducted for the first time after an engine operation start, there is a possibility of a big racing occurrence due to a response delay in oil pressure in the engagement side.
The present invention has an object of stably restraining an occurrence of racing without cost-up and prolongation of a speed change period in an automatic transmission for carrying out a speed change by controlling a back pressure of an accumulator.
To achieve the above object, according to the present invention, the construction is such that, in an automatic transmission provided with an accumulator disposed in an oil pressure supply pipe in each of friction engagement elements, at least one of the accumulators in the friction engagement element to be engaged and in the friction engagement element to be released, is increased in stepwise in response to a speed change request, when a racing is detected during a speed change.
The other objects and features of this invention will be understood from the following description with reference to the accompanying drawings.